1. Field of the Invention
The invention relates to environmental pollution control. More particularly, the invention relates to a method for removing and recovering volatile contaminants from wastewater.
2. Description of Other Relevant Methods in the Field
A number of methods have been developed to remove volatile contaminants such as hydrocarbons from chemical plant and refinery wastewater i order to render it safe for discharge into the surface and ground water supply. The development of these methods has been driven by the discovery that water sources proximate to industrial areas have become contaminated with volatile organic compounds such as benzene, toluene, chlorinated and halogenated solvents and other compounds derived from petroleum.
A common method used in the petroleum industry for removing volatile organic compounds from wastewater has been to air strip the wastewater in a packed tower. Stripping is carried out in a vertically oriented tower at atmosphere pressure. Contaminated wastewater is pumped into the upper portion of the packed tower and cascades downwardly through liquid-gas contacting media referred to in the art as packing. In the alternative, a series of contacting trays may be substituted for the packing. Air is forced upwardly through the packing by means of a blower or fan to volatilize organic compounds. The contaminant free wastewater is collected at the bottom of the tower and is removed for disposal consistent with any remaining contamination. The contaminant laden air is released from the top of the tower to the atmosphere. In the alternative, the air is collected and purified to reduce hydrocarbon content before release to the atmosphere.
A number of methods have been developed for separating hydrocarbon for pollution control. U.S. Pat. No. 4,054,429 to N. Ostojic et al. teaches a method and apparatus for recovering solvent from a gas such as air. By the method, solvent contaminated air is passed through an oil absorber which absorbs the solvent, producing a clean air product. The oil-solvent mixture is stripped with inert gas to produce a solvent free oil. The remaining inert gas-oil mixture is separated by first condensing the oil and then passing the inert gas through an activated charcoal filter which removes last traces of solvent from the inert gas. Cleaned inert gas is returned to the stripper for recycle in the oil-solvent stripping stage.
U.S. Pat. No. 4,755,499 to L. G. Neal et al. teaches a sorbent for removing nitrogen oxides, sulfur oxides and hydrogen sulfide from gas streams. The sorbent comprises an alumina substrate having a pore volume between 0.4 and 0.8 cc/gm and an alkali or alkaline earth component.
U.S. Pat. No. 3,864,450 to T. Takeyama et al. teaches a sorbent for remaining nitrogen oxides from gaseous mixtures. The sorbent comprises carbon impregnated with sodium hydroxide or potassium hydroxide.
U.S. Pat. No. 4,495,056 to D. G. Venardos et al. teaches oil shale retorting and a retort water purification process. Retort water is steam stripped, carbon adsorbed and biologically treated followed by activated sludge treatment. The purified retort water is reused.